I'm probably not the only one to make this suggestion, but something I think would give the modding community a lot of power, not to mention a reason to switch to modding using datapacks, would be to allow command outputs to be written to a file. I can't be the only one who's realized you could write a server application to modify datapacks live and reload them in-game without affecting up-time. This gives developers a lot of power to build a more dynamic experience in-game, being able to utilize tools outside of Minecraft and directly impact the world and the players. However, some of the cooler ideas I've had doing something like this would require I be able to see what players are up to outside of the game.
I might have a server application that "listens" to the game by reading a Command Output file. Maybe it's listening for outputs where players successfully complete some achievement or pick up a certain item. The application would then check the relevant player names and bounce it off a database, updating the database with pertinent information. So now people on a website, that also checks that database, would be able to see, live, which players have earned server currencies or complete some achievement.
And to add to that, you could also imagine that a server application might check the database for relevant information (say, chat history on the website), and write to file commands to be run in-game.